[CentOS-virt] Test new xen, centos-release-xen and kernel for auto grub update on kernel install

[Johnny Hughes]

The new process for auto updates of grub upon kernel install is in the
xen4centos testing repo.

In order to test these as updates to an existing system, you can do this:

1. download the test repo file:

http://dev.centos.org/centos/6/xen-c6-RC1/xen-c6-RC1.repo

2. Put it in /etc/yum.repos.d/

3. Issue this command:

yum --disablerepo=Xen4CentOS upgrade xen\* centos-release-xen

(that should install all the new files required to make the kernel
update work automatically)

4.  Review the new file /etc/sysconfig/xen-kernel ... if there is any
other items you want on the 'kernel /xen.gz' line, you would edit the
file.  For example, I like to add  'com1=115200,8n1 console=com1' to the
end of that line so I can use consoles in virsh.  So I would change the
line:

XEN_KERNEL_MBARGS="--mbargs=dom0_mem=1024M,max:1024M loglvl=all
guest_loglvl=all"

to

XEN_KERNEL_MBARGS="--mbargs=dom0_mem=1024M,max:1024M loglvl=all
guest_loglvl=all com1=115200,8n1 console=com1"

(both of those should be one line if they wrap)

This is also where you can assign more or less memory to the dom0. etc. 
This article has some other possible parameters for the xen.gz line:

http://www.informit.com/articles/article.aspx?p=1187966&seqNum=4

5.  Make sure this is set as well in /etc/sysconfig/xen-kernel:

BOOT_XEN_AS_DEFAULT="yes"

6.  issue this command to upgrade the kernel:

yum --disablerepo=Xen4CentOS upgrade kernel-\*

7. This should upgrade your kernel and it should also automatically
update your /boot/grub/grub.conf to boot for dom0 use.

If, for some reason, you want to manually upgrade the grub.conf file
yourself, set the BOOT_XEN_AS_DEFAULT to "no" instead of yes.

8.  If you want to install the xen kernel in other places other than xen
dom0 machines, just  make sure not to install the xen package, and
grub.conf will get standard and not xen kernel boot entries.

====================

Once ypu have done your updates, please delete 
/etc/yum.repos.d/xen-c6-RC1.repo

===================

Please report positive and negative experiences here so we can move this
into the CentOS-6 xen4 repository (or fix things that are broken).

Thanks,
Johnny HUghes


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